Which orbital class rocket (active or retired) has the highest thrust to weight ratio at liftoff?

  • $\begingroup$ I thought this had been asked before, but if has, I could not find it. $\endgroup$ Sep 21, 2022 at 18:04

3 Answers 3


Seems like JAXA's SS-520 with launch mass of 2,600 kg and 14,600 kgF average thrust would have TWR of about 5.6

data found here

  • 1
    $\begingroup$ Video of launch here - youtu.be/OeW-Qqu9-8U?t=28 6 G acceleration? $\endgroup$ Sep 22, 2022 at 13:59
  • $\begingroup$ The only SS-520 that successfully completed an orbital mission was fitted with a 78kg third stage. Additionally, the original paper reports a 14.2 ton average vacuum thrust, using some ideal rocket theory and the papers data the sea level thrust would be about 12.7 ton rounded up, i.e. 12.7/2.678 = 4.74 TWR (admittedly the paper is from 1982 and the orbital flight using the SS-520 was in 2018, so not entirely unlikely they improved the thrust) $\endgroup$
    – Ruben
    Sep 22, 2022 at 18:51
  • $\begingroup$ To be fair, I cannot find any specification for the Mu-3H thrust data so it might as well be vacuum thrust too. Consequently assuming a similar correction for the Mu-3H thrust, the SS-520 used for the TRICOM-1R launch would still have the highest TWR $\endgroup$
    – Ruben
    Sep 22, 2022 at 18:55
  • $\begingroup$ Ah, this is one of the Japanese ones which does its gravity turn at T-∞ :-D $\endgroup$ Sep 25, 2022 at 22:28
  • $\begingroup$ @JörgWMittag Not really -∞, just T-(couple hours) when the erector is angled to the launch angle ;) $\endgroup$
    – SF.
    Sep 26, 2022 at 11:19

I took the data from the JSR Launch Vehicle Database, available here. This includes take-off thrust and launch mass, so the Thrust-to-Weight Ratio was easily calculated. Unfortunately this list also includes many missiles and sounding rockets and I was too lazy too properly filter them with some other list of orbital class launch vehicles. However, eyeballing the list for orbital class launch vehicles with successful non-test missions, the Mu-3H seems to be the highest. It has a TWR of about 4.9, which certainly is quite high. Most of the Mu-family rockets have very high TWR.

After some further digging on the Mu-family I found a source in Japanese with sea-level thrusts and another (in English) with take-off mass for each configuration of the Mu-family rockets, which gives the following TWRs:

  1. 4.74 - M-3C
  2. 4.57 - M-3S/M-3H
  3. 4.52 - M-4S

Assuming that the question refers to thrust to "total vehicle" weight ratio, I would opine that the ratio is determined by the mission. A heavy launch-to-orbit vehicle would be loaded to get the heaviest load to space and have a low thrust to weight ratio. An anti-missile missle would have a high thrust to weight ratio to accelerate rapidly and get to an approaching missile as far away from it's target as possible. I don't see any value in this parameter as a figure of merit.

  • $\begingroup$ Using a high thrust to "total vehicle" weight ratio would result in a very rapid acceleration of the rocket and thus would require a stronger and heavier rocket structure. Also the payload structure should resist the rapid acceleration and would be heavier. $\endgroup$
    – Uwe
    Sep 23, 2022 at 18:15
  • $\begingroup$ Somebody asks: "Which animal runs the fastest?" You telling them: "I don't see any value in speed as a parameter for classifying animals" is not a useful answer $\endgroup$
    – Ruben
    Sep 24, 2022 at 15:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.